Machines that continuously and automatically produce large quantities of flake ice for use by the food processing industry, for cooling concrete in construction, and other uses are well known. A common type of conventional ice-making machine utilizes a stationary cylindrical drum that has an outer surface exposed to a coolant or a refrigerant and an inner surface onto which water is introduced. The water is frozen on the inner surface of the drum and removed by a rotating array of blades to form large flakes of ice. Such machines are capable of producing substantial quantities of ice, but are relatively large and expensive to construct.
Flake ice machines have also been developed that utilize a rotating cooling disk, rather than a drum, for more efficient production of ice. One such example is the disk machine disclosed in U.S. Pat. No. 3,863,462 to Treuer. A non-evaporative refrigerant flows through a pair of geometrically complex flow passages formed within the disk. Water is applied to a portion of the planar outside surfaces of the rotating disk, is subcooled, and is then removed by a series of radially spaced blades positioned adjacent the outer disk surfaces.
Other conventional rotating disk ice machines use a greater number of internal flow passages of generally equal length in an attempt to provide uniform cooling of the entire outer disk surface. Refrigerant flowing into the disk is channeled to provide each passage with a substantially equal amount of refrigerant. However, in practice it has been found that slight differences in the length of the passages, manufacturing variations in the cross-sectional dimensions of the passages, and varying refrigerant pressure losses associated with different passage contours results in an uneven degree of cooling from each passage.
Refrigeration circuits for conventional disk machines supply refrigerant to the disk at a flow rate that is limited to ensure that all refrigerant is evaporated within the disk. Substantially all refrigerant leaves the disk as a super-heated vapor. This type of construction and operation of a disk cooling system results in the most cooling-efficient flow passages within the disk not being fully utilized. The refrigerant flow rate must be restricted to a rate corresponding to the rate of evaporation within the passage with the least cooling capacity to ensure substantially all refrigerant is evaporated within that least efficient passage. But flow passages with more efficient rates of evaporation (i.e., that absorb more heat from the liquid material being frozen) are also limited to the flow rate corresponding to the less efficient passages, and thus are underfed refrigerant.
In addition to the capacity limitations of conventional ice-making machines, another drawback of conventional drum and disk machines is the variation in quality of the ice produced. In order to assure proper separation of the ice from the machine's cooling surfaces, to prevent the ice flakes from sticking together, and to produce ice flakes of a desirable large size, it is necessary to add a small quantity of salt to the water that is being frozen. Conventional machines rely on the manual addition of salt at periodic intervals to a water reservoir. This batchwise addition of salt results in a fluctuation of the salt concentration in the water, and inconsistent quality of the ice produced.
Additionally, the ice removal blades used in conventional machines of either the disk or drum type must be mounted spaced away from the machine's cooling surfaces to accommodate rotational run-out of the cooling member without causing the cooling surfaces to wear.